1. Field of the Invention
This invention relates generally to manufacturing of electronic circuits in which solder connections are utilized to make connections to a circuit chip substrate and is directed in particular to an apparatus and method for securing the chip substrate during wet processing such as cleaning.
2. Description of Related Art
Forming an electronic package whereby an electrical component such as a multilayer ceramic package or circuit chip substrate is electrically connected to a substrate such as a card, a board, another connector and any other electronic part is well known in the art. Surface mount technology (SMT) has gained acceptance as a preferred means as joining electronic devices together, particularly in high end computers. As circuit densities increase there is an increased demand for more I/O and the interconnections which are solder bonded must be smaller and more closely spaced.
Numerous solder structures have been proposed for surface mounting. Typically the surface mount process is performed by screening solder paste on conductive metallic pads exposed on a surface of a first electronic structure or substrate. A stencil printing operation is used to align a contact mask to the pads. Other known surface mount technology uses solder balls rather than solder paste to provide the solder connecting structures. This technology is known as C-4 and, by using such solder balls, a more exact and somewhat greater quantity of solder can be applied than can be applied through screening. Another type of solder interconnection is cast solder column which is mainly used to connect a multilayer ceramic package to a board. The method of utilizing solder balls is also know as ball grid array or BGA, while the method of utilizing solder columns is generally referred to as column grid array or CGA.
When solder columns or balls are joined to ceramic substrates, a solder flux such as a rosin is typically used to remove oxides from both substrate and column or ball surfaces. This prevents or reduces oxidation from the joining surfaces when they are subjected to elevated temperatures for soldering, thereby serving to maintain the solderability of the substrate and solder columns or balls. If there is any flux residue left on the substrate surface, corrosion may result.
It has been a problem in the prior art to remove residual flux, which problem has typically been solved by utilizing solvents. It has been found that a major problem associated with the above processes is in supporting the substrate vertically in a manner that will prevent damage to the solder balls or columns during the cleaning cycle. Such cleaning cycles and other processing which utilizes liquids is generally referred to as wet processing.
Conventional fixturing utilized in the past has typically supported substrates by utilizing open space between the edge of the substrate and the edge of the balls, columns or pins. This has allowed the parts to be held by the substrate body, thereby preventing the balls, columns or pins from making contact with the fixture body. However an increasing number of electronic structures have reduced the distance from the substrate edge to the first row of columns or balls. This is typically been 0.025 inches (0.63 mm)for CGA product and 0.015 inches (0.38 mm) for BGA product. This reduction in space along with typical variations in substrate tolerance has made it difficult to utilize conventional fixturing to support the substrates during wet processing.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an improved apparatus and method of supporting substrates utilizing solder connections during wet processing.
It is another object of the present invention to provide an apparatus and method for supporting substrates having solder connections which does not utilize or support the substrate in the space between the edge of the substrate and the first row of columns or balls.
It is yet another object of the present invention to provide an apparatus and method of securing substrates having solder connections which may accommodate different sizes of substrates.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.